1. Field of the Invention
This invention relates to a spread roller assembly including a pair of juxtaposed rollers for spreading a processing liquid across a layer of an exposed film unit so as to initiate the formation of a visible image therein.
2. Description of the Prior Art
Spread roller assemblies for use with cameras of the self-developing or instant type are generally well known. A common type of such an assembly includes a pair of juxtaposed elongate rollers which may be manually driven by pulling an exposed film unit through the rollers or they may be powered by a motor mounted within the camera. Examples of the former may be found in U.S. Pat. Nos. 3,745,904, 3,327,599 and 2,794,378 while examples of the latter may be found in U.S. Pat. Nos. 4,134,655, 4,087,831 and 4,078,241. Often, the rollers are rotatably supported by individual bearing blocks located at each side of a spread roller housing and a biasing means including at least one spring is provided for resiliently biasing one of the rollers toward the other, as described in the aforementioned U.S. Pat. Nos. 3,745,904 and 3,327,599.
The biasing arrangements used in U.S. Pat. Nos. 3,745,904 and 3,327,599 are capable of exerting side forces on the respective spread roller assemblies, i.e., forces which are not substantially perpendicular to the axes of the rollers. Such side forces may change the substantially parallel relation between the rollers and adversely affect the spreading of a processing liquid across a layer of an exposed film unit. Further, the biasing arrangement disclosed in U.S. Pat. No. 3,745,904 unnecessarily increases the amount of power required to rotate the roller because the ends of the springs are in direct engagement with the journals of one of the rollers.
It is also well known to construct spread roller assemblies of the type described such that they may be operatively attached to their housings without the use of screws, rivets or other conventional means. Such assemblies may be classified as being of the snap-in type, e.g., see U.S. Pat. No. 3,974,510 and the aforementioned U.S. Pat. No. 3,745,904. While this type of snap-in assembly works well, it does have its disadvantages. For example, the structure for supporting the rollers is usually of a unitary construction and if a portion of the structure is out of specification then the entire structure has to be replaced. Further, this structure often takes the form of a U-shaped bracket wherein the biasing means exerts forces on the base and legs of the U thereby giving rise to the possibility that the spring may exert side forces on the legs, as mentioned hereinbefore.
In combination with spread roller assemblies of the above type, it has been found beneficial to provide the camera with means for releasably retaining the exposed film unit after it has been ejected by the spread rollers. Such a means is shown in the aforementioned U.S. Pat. No. 4,134,655 in the form of a pair of laterally spaced clips which cooperate with a wall of the camera for grasping an exposed film unit by its trailing end after it has moved out of engagement with the spread rollers. However, since these clips are in frictional engagement with the film unit throughout most of the time that it is passing through the rollers they create at least two problems. Specifically, these clips increase the forced required for the rollers to advance the film unit toward the exterior of the camera. Also, if the stiffness of these clips exceeds a certain point, they may cause the advancing film unit to buckle at a point betweem their engagement with the film unit and the bite of the spread rollers thereby possibly adversely affecting the spread of the processing liquid.